1. Field of the Invention
The present invention relates to an electrostatic type image forming apparatus using a charging device for forming electrostatic latent images on a latent image-bearing meter such as used in electrophotographic copiers, electrophotographic printers, electrophotographic facsimiles and the like.
2. Description of the Related Art
In the field of charging devices used with electrostatic image forming apparatus, there are well-known techniques for using projection electrodes for the purpose of reducing the amount of ozone generated and improving charging efficiency.
Charging devices using projection electrodes discharge from the tip of the projection electrode. Thus, the discharge concentrates in a direction facing the tip of the projection electrode, and, therefore, the area near the tip of the projection electrode is more strongly charged relative to other areas. When a projection electrode is used, therefore, the charge state differs depending on the location, so as to cause so-called nonuniform charging. When nonuniform charging occurs, image defects occur such as irregular image density and the like.
The ozone generated during discharge by the charger causes deterioration of the charge-receiving member such as a photosensitive member and the like, and as a result causes image defects. When a projection electrode is used, the amount of ozone generated is slight compared to the amount generated when a wire electrode is used, and better images can be formed when less ozone is generated.
The generation of nitrous oxides (NOx) is affected by the discharge from the tip of the projection electrode, and nitrous oxides may adhere to said tip of the projection electrode. When NOx adheres to the tip of a projection electrode, the edges of the latent image become dim and blurred, and the image may be erased, resulting in so-called image drift. Furthermore, when the tip of the projection electrode becomes corroded by the nitric acid produced by the NOx, image defects result due to nonuniform charging as a result of inadequate discharge.